This invention relates to a helical scanning magnetic recording/playback device suitable for digital magnetic recording/playback data on a magnetic tape by helical scanning using a recording head and playback head provided on the periphery of a rotary head drum.
Conventionally, for example, a U-tape loading mechanism of helical scanning digital magnetic recording/playback devices has been structured as shown in FIG. 13.
In detail, a magnetic tape 4 wound on a supply reel 2 and a take-up reel 3 in a tape cassette 1 attached at the place is drawn out from the tape cassette by a tape loading mechanism 6 having a loading ring 5, and is loaded on the peripheral surface of a rotary head drum 7 in a U-like shape helically.
At this time, the tape loading mechanism 6 rotates the loading ring 5 in the arrow direction a, thereby, magnetic tape 4 is wound on the periphery of the rotary head drum 7 by a plurality of rotatable guides 8 fixed on the loading ring 5. Simultaneously, draw guides 9 and 10 on both sides move to the arrow directions b and c respectively to draw the magnetic tape 4, whereby the magnetic tape is loaded.
Through the tape loading, the magnetic tape 4 is passed on a capstan 11, full width erasing head 12, audio recording/playback head 13, channel erasing head 14, and a plurality of fixed guides 15. The loading mechanism is structured so that the magnetic tape 4 is moved helically around the periphery of the rotary head drum 7 by the aid of a pair of fixed guides 15 provided at the tape inlet 16 and tape outlet 17 those are the entrance to and exit from the rotary head drum 7 for the magnetic tape.
After completion of the tape loading operation, a pinch roller 18 mounted on the loading ring 5 presses the magnetic tape 4 against the capstan 11 in the arrow direction d, and the magnetic tape 4 is moved at a constant speed in the arrow direction e along the running route while the magnetic tape is taken up from the supply reel to the take-up reel. While running of the magnetic tape 4, data on the magnetic tape is recorded/played back in digital magnetic helical scanning record/playback method by the rotary head drum 7 which is rotated at a high speed in the arrow direction f.
A conventional rotary head drum 7 of helical scanning digital magnetic recording/playback devices of this type is typically structured as shown in FIG. 14.
In detail, a set of components comprising an erasing head ER (A/B) and recording heads REC (A) and (B), and the other set of components comprising an erasing head ER (C/D) and recording heads REC (C) and (D) are provided differently in azimuth and central-symmetrically facing each other. Similarly, a set of playback heads PB (A) and (B) and the other set of playback heads PB (C) and (D) are provided differently in azimuth and central-symmetrically facing each other. The playback heads PB(A), PB(B), PB(C), and PB(D) correspond to the recording heads REC(A), REC(B), REC(C), and REC(D) respectively. Each playback head PB is positioned apart angularly from the corresponding recording head REC with a certain angle.
As shown in FIG. 15, the track width W1 of the playback heads PB(A), PB(B), PB(C), and PB(D) is the same as the track width W2 of the recording heads REC(A), REC(B), REC(C), and REC(D).
A shown in FIG. 15, the magnetic tape 4 is moved at a constant speed in the arrow direction e while the rotation drum 7 is rotated at a high speed in the arrow direction f, and data are written on recording tracks T1, T2, T3, and T4 of the magnetic tape 4 in helical scanning style by recording heads REC(A), REC(B), REC(C), and REC(D).
For playback, data on the recording tracks T1, T2, T3, and T4 are read by the corresponding playback heads PB(A), PB(B), PB(C), and PB(D) in the relation of one-to-one correspondence.
However, recently the narrow track has been popularized in the field of the helical scanning magnetic recording/playback device. The improvement in machine accuracy of a travel motion system such as rotary head drum 7 and magnetic tape 4 and the improvement in performance of a servo system are required for accurate tracking during playback, but enormous expenses are necessary for such improvement.
In some helical scanning magnetic recording/playback devices, signal areas exclusive for tracking are provided on the recording tracks T1, T2, T3, and T4 on the tape format, but such method is involved in a problem that the recording wave length is lost due to increased data rate.
Otherwise, in some conventional helical scanning magnetic recording/playback devices, when the traveling speed of a magnetic tape 4 is changed for variable speed playback, the rotation speed of the rotary head drum 7 is changed corresponding to the traveling speed of the magnetic tape 4. As a result, data on all recording tracks T1, T2, T3, and T4 of the magnetic tape 4 is read by the playback heads PB(A), PB(B), PB(C), and PB(D).
However, this method is involved in a problem of the response capability of the servo system for the rotary head drum 7 when the speed is changed. In addition, this method is involved another problem that the variation of the rotation speed of the rotary head drum 7 causes the change in air film thickness formed between the peripheral surface of the rotary head drum 7 and the magnetic tape 4 to result in insufficient contact of the magnetic tape 4 to the playback heads PB(A), PB(B), PB(C), and PB(D).
Otherwise for variable speed playback, in some conventional helical scanning magnetic recording/playback devices, dynamic tracking heads which are vibrated vertically at high frequency are used as the playback heads PB(A), PB(B), PB(C), and PB(D) so that not all data on recording tracks T1, T2, T3, and T4 but partial data of the magnetic tape 4 is read without varying the rotation speed of the rotary head drum 7 when the traveling speed of the magnetic tape 4 is changed. However, the dynamic tracking head is expensive and the servo circuit is complex, therefore, this method is involved in a problem of high cost.